A string is attached to a wall and vibrates back and forth, as in Figure 17.18. The vibration frequency and length of the string are fixed. The tension in the string is changed, and it is observed that at certain values of the tension a standing wave pattern develops. Account for the fact that no standing waves are observed once the tension is increased beyond a certain value.

Question

A string is attached to a wall and vibrates back and forth, as in Figure 17.18. The vibration frequency and length of the string are fixed. The tension in the string is changed, and it is observed that at certain values of the tension a standing wave pattern develops. Account for the fact that no standing waves are observed once the tension is increased beyond a certain value. 
a) The frequency of vibrating cycles is sufficiently high that they all cancel each other. 
b)The time required to create a new wave cycle does not equal the time taken by a cycle to travel the entire length of the string. 
c) When the tension is increased beyond the value for which = 2L, the string cannot contain an integer number of half wavelengths. 
d)Repeated reinforcement between newly created cycles causes a zero amplitude standing wave.

I think when the frquency is sufficiently high they'll cancel out, because frequency if proportional to tension.

Please check my answer

Your answer is wrong.

http://hyperphysics.phy-astr.gsu.edu/hbase/waves/string.html

What happens if Tension gets greater than the FIXED vibration frequency?

the string will obviosly break DUH!!!

so i think the answer will be d.